Cream together butter, shortening, sugar, and pudding.,Add eggs in one at a time.,Add in sour cream and vanilla. Mix well.,Sift together flour, baking powder, and salt.,Add flour mixture into butter mixture alternately with milk starting and finishing with flour mixture.,Pour into well greased and floured 13x9 pan.,Bake at 350 for 40-50 minutes.,Variation for White Cake: Use 4 egg whites instead of the 3 whole eggs.,______,Variation for Chocolate Cake: Use chocolate pudding mix and 1/3 cup cocoa. (I then up the milk a little.).